Link Layered Networks With Improved Operation

ABSTRACT

A method and system for optimizing and keeping operational a wireless link layered network in which a system control and modifying message (SCMM) is elicited from nodes receiving information packets and based upon whether the node originating the SCMM is from a link layer level which is equal to or less than the link layer level eliciting the SCMM, rerouting or adjusting future transmissions can be effected or items like a less current time at a receiving node and a most recent utilization rate of a receiving node can be adjusted, recorded or set.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division under 35 U.S.C. § 120 of copendingapplication Ser. No. 13/297,431, filed Nov. 16, 2011, which is adivision of application Ser. No. 10/950,368 filed Sep. 24, 2004, nowU.S. Pat. No. 8,072,945.

FIELD OF THE INVENTION

The present invention is generally in the field of wirelesscommunication networks, especially the field of security, machine tomachine (M2M), and emergency wireless communication networks and morespecifically, improvements in wireless link layered networks.

BACKGROUND OF THE INVENTION

The art of wireless communications and its use in emergency, M2M, andsecurity networks has been well developed. In a sub-segment of thetechnology, also known as mesh networks, subscribers units are used byother units in the network as repeaters thus building a networkproviding communications from each of the remote subscriberstransceivers to a central or collection transceiver. In most instances,the communication paths from each subscriber to such a central unit arefixed and determined during the commissioning of the whole network. Suchsystems are described, for instance by Burns (U.S. Pat. No. 5,129,096).Such fixed systems have a number of disadvantages, namely, they do notpossess autonomous routing reconfiguration capabilities, when for onereason or another, subscribers drop out of the network, eithertemporarily or permanently, and require the intervention of an operator,to reestablish network integrity through the establishment of newcommunication links using the remaining resources (subscribers) in thenetwork.

In U.S. Pat. No. 5,455,569 (hereby incorporated by reference and termedthe '569 patent), the present inventor described a link layered wirelesscommunication network that overcomes the shortcomings encountered infixed communication paths wireless networks. particularly, said linklayered network, automatically, and without the intervention of anoperator, reconfigures the optimal communication paths when externalparameters change over time. Typically such a reconfiguration willresult in a routing having the minimal possible number of hops between aremote node and the central node.

However, it has been found that under some special circumstances,improvements to the teachings of '569 are required. For instance, thenetworks described in '569 were originally used mostly for securitysystems, such systems involve only minimal communications, since onlyalarm states and infrequent routing updates messages are required. Moremodern link layered networks have now found applications in a greatvariety of circumstances, and with new challenges, not contemplated in'569, nor in the present inventor's U.S. Pat. No. 5,974, 236(hereinafter '236). For instance, link layered networks associated withdata based systems such as systems of vending machines, require updatingnot only of alarm systems, but a constant stream of data related toinventory levels and machines status; thus optimization of systemthroughput becomes important. Furthermore, the addition of newsubscribers to existing networks have increased the number of nodes(each node is associated with such a new subscriber and thus includesits own transceiver) in a network, thus increasing the radio messagetraffic within a network. Furthermore, such network expansion wouldoften involve more modern nodes having greater capacities andcapabilities, necessitating new approaches to network throughputoptimization. It is possible that a system of “mixed” nodes will degradeover time as the variation in the nodes increase. In addition, thispotential degradation of the network will be the primary reason for thesystem to fail because the optimizing algorithms in place for years ordecades could not anticipate variations unknown at the time thealgorithms were written.

Link layered networks are now also used in sub-metering systems,whereby, means are provided to meter energy utilization (and demandrate) for a given location (i.e. an office building with multipletenants), as well as the usage and demand rate for each tenant, and saidmeans are interfaced each to a communication node that reports thatinformation first to the node associated with the central meter (toascertain correct summation of demand and utilization), and from thereto a “command center.” That command center can be either the utilitycompany itself, or even an energy management system associated with thebuilding and engaged in load optimization. Such communications betweenthe central metering system at each such location and a command centermay involve the use of other subscribers, which are not necessarily apart of the meter reading network. There is therefore a need to providefor optimized network throughputs in networks containing nodes ofdiffering capacities and capabilities.

Other applications of link layered network also involve both mobile(such as taxicabs) and stationary “points of sales” where credit cardsreaders are networked into a link layered network reporting to a centralnode. As is the case with submetering systems, there is a need toprovide for optimized communications to a central node, often usingsubscribers having nodes of diverse capacities.

The prior link layered network art ('569 and '236), while teachingadequately how individual nodes can be dropped from, or incorporated ina network, fails to provide for special cases, for instance when a wholenetwork is shut down. As the numbers of, as well as the density of nodesin a link layered network are increased, particular problems areencountered, for instance, recovery of a network from an extreme state.An extreme state could result from local power failure, rolling blackouts, or even the intentional shut down of a network for variousreasons. In the prior art, when such a system is “awakened” after such afailure, many of the nodes, simultaneously, seek to reestablish theirbest routing by sending out messages that elicit responses fromneighboring nodes, thus allowing the re-incorporation of a node into thenetwork. In such larger networks, one runs into the problem of excessivetraffic and thus congestion, and failure to timely reestablishcommunication links, particularly after power outages or intentionalshut down of the network, when all subscribers, almost simultaneouslyseek to reestablish communication routes to the central transceivernode. There is therefore a need for an optimized method of restarting anetwork without encountering such radio traffic congestion.

Furthermore, new subscriber additions also bring about networks thathave transceivers of different capabilities, capacities andcharacteristics, necessitating both optimization of throughput as wellas routing in such networks. Typically, newer technology will havegreater capacity per nodes (where capacity is understood to be the sizeof each packet transmitted). Flammer in U.S. Pat. No. 6,480,497,attempts to optimize net throughput in mesh networks by modifying signalcharacteristics in response to determining performance metrics of thelast received signal, over a given link between two nodes. This approachhas three major shortcomings. Firstly, optimization is carried out onlyon each link, and the teachings do not assure that such optimizationwill necessarily result in overall network optimization, since theoptimization of throughput process on each link itself may simply add alarge number of additional unnecessary hops. A second shortcoming isthat in link layered networks of the present invention, it is necessaryto adapt the system to such signal characteristics variations betweennodes, rather than modifying them as Flammer '497 suggests. A thirdshortcoming of a system of the type described in '497 is that it lacks“directionality” and does not possess “sequentiality” of theoptimization process of each link between any two nodes. Thus, often, anoptimizing process of the link between any two nodes may requirere-optimization of neighboring links causing incessant systemoscillations and excessive radio traffic in the network. There istherefore a need to optimize routing of packets in link layered network,despite having incongruity in nodes packets capabilities and capacities,such as baud rate and packet length, and therefore consolidate in onesingle network nodes of vastly different characteristics. There isfurther a need for such an optimization process which will not by itselfthrow the network into constant oscillations and readjustments.Furthermore, such optimization should promulgate within the wholenetwork, standards generated from the then designated central node.

Flammer et al in U.S. Pat. No. 5,488,608 (the '608 patent) suggests thattraffic in a network can be routed, without having a network directoryat each node, and indeed, when intermixing older technology with newertechnology in link layered network, there are practical limitations onlocal memory, preventing sometimes, storing all possible routingsbetween any two points at each node (as taught in the present inventor'sU.S. Pat. No. 5,974,236). However, the '608 approach relies on assigningto each node an identifier indicative of the nodes coordinate locations,and using those coordinates for facilitating routing of packets to andfrom such nodes. This approach, however will not work, when part of thenodes have variable geography, such as mobile nodes contemplated in '236and the present invention, nor will that approach work when the linklayered network is, for instance a submetering network, where all thenodes are typically, essentially, at the same location or in the samebuilding.

The lack of information on the link layer level in the header of the'608 packets will often result in packets being transmitted almostrandomly, till they find the destination node to which they wereintended, or worse, result in circular transmissions (where the samepacket is handled between a sub group of all nodes that does not includethe destination node, in essence repeatedly) causing unnecessary radiotraffic congestion in the network. There is therefore a need to providefor a link layered network in which circular transmissions and radiotraffic overload is avoided, that does not rely on the specificknowledge of the coordinates of each of the nodes in the network, andoptimizes and accommodates future, currently unknown nodes yet to beimplemented on the network.

When a practical link layered network is installed, some of its nodes,by virtue of their geographical location, height and type of antenna,level of RF noise and interference, or even universality of capacity, ora combination of these factors, become preferential repeaters. Suchnodes can be termed “Critical Nodes” in that they serve as a hub for alarge number of routes from remote transmitters to the then designatedcentral node (from here on we will term this the “central node”, but itshould be understood that according to the teachings of '236, any nodein the system can be designated the “then central node” withoutinterfering with the operation of the system).

Such critical nodes in the prior art would thus become overloaded andtransmit from remote nodes to the central node a disproportionate amountof the network's messages, creating a localized over utilization of theavailable broadcasting spectrum, and in some cases, these result in lossof packets. There is therefore a need to equalize the traffic load toother less critical nodes, even though, some messages will no longer betransmitted with the minimum number of hops, as taught in '569 and '236,but be optimally transmitted, so as to optimize both the utilization ofthe various nodes and the radio channel. This by spreading thetransmissions over a wide geographic area in the system as well asallowing the number of hops required to transmit a packet from a remotenode to the central node to be greater than minimal.

OBJECTS OF THE INVENTION

It is a major object of the present invention to provide for a linklayered network that consolidates within it nodes having vastlydifferent capacities, yet, optimizing routing within said network toaccommodate such differences.

It is yet another objective of the present invention to provide optimalspectrum efficiency utilization within a certain geographical area byminimizing system management traffic, or transmissions, and byequalizing geographical distribution of transmission, particularlylowering the load on critical nodes in the network.

It is a further object of the present invention to provide methods ofincreasing link layered network throughput by optimizing routing ofmessages, not just by minimizing the number of hops each message issubjected to in order to reach its destination, but making suchoptimization scheme dependent also on the specific messagecharacteristics. This rather than modifying a message's or a signal'scharacteristic.

It is yet a further object of the present invention to provide in a linklayered network, a method of preventing network oscillations.

Yet another object of the present invention is to provide methodspreventing transmission congestion upon restarting of networks to post ablack out, a rolling black out and or intentional shut down of thenetwork, by providing a stratified randomization process allowing thegradual reestablishment of the network rather than a simultaneousattempt to reestablish routing which results in excessive trafficcongestion.

It is a general object of the present invention to provide for networkoptimization by optimizing nodes operational parameters and routingexpansively, namely, in a direction from the central node to the mostremote nodes, thus keeping at all times at each node optimal operationalparameters and routing lists that minimizes message hops while keepingrational geographical distribution of transmissions and providing forvastly different nodes (and thus packets or message) characteristicswithin the network. It is also an object to obviate the drawbacks ofearlier systems as described.

SUMMARY OF THE INVENTION

These objects, and others which will become apparent hereinafter, areattained in accordance with the present invention by the judicious useof a System Control and Modifying Message (hereinafter SCMM) and anumber of algorithms executed at each node, some in response to thereceipt of such an SCMM, others in response to changes in the network.Said SCMM is sent in lieu of normal acknowledgment of receipt of apacket in response to the successful receipt of a packet by any node inthe system.

The SCMM contains the most recent information on the node that sent thatSCMM, including, but not limited to, the time at the acknowledging node,the power level of the transmission (as set at the acknowledging node)as well as the received signal strength, the capacity of the node(packet length), and the most recent utilization rate of the node.

The SCMM also contains information as to the node's current link layerlevel, the deviation from the standard network frequency the lastmessage was received at, the unique identity of the node sending theSCMM as well as who the SCMM is targeted to (though other nodes can anddo “hear” that SCMM and act on some of the information contained in theSCMM, as will become clearer below). Additionally, the SCMM contains a“packet sequence number” that acts as a unique identifier of thatpacket, here the packet is the received packet to which the SCMM is anacknowledgment.

The packet sequence number is used to prevent loop formation, whereby apacket is transmitted in the network and is returned to the sending nodefor retransmission. It should be appreciated that while an SCMM is apacket as well, since it is always an acknowledgment it does not have apacket sequence number, only “data packets” have such an identifyingnumber.

It should be understood that the central node may not be the point ofuse of the information or data included in the packets received by it.The central node may communicate the information via other means (notthe link layered wireless network itself) to a data collection, datareview or a command center, where such data may be acted on. Such othercommunication means may include land lines, other public wirelessnetworks, LAN or WLAN, or even an internet connection. It is quitepossible, and sometimes desired, that such communication means bechanged during the operation of the whole system, and such a changeovermay dictate a change in the optimized routing of messages fromsubscribers nodes to the central node. For instance, if the capacity totransmit information to such a command center is changed due to achangeover in the communication means between the central node and thepoint of use of the data transmitted from the link layered network. Ifsuch a change were to occur, it would be communicated through the SCMM,for instance by identifying a new packet length, more compatible withthe said communication means transmission capacity.

In general, the central node, having a link layer level, would receive amessage addressed to it from a subscriber unit, and the last hop fromthe network to the central node would typically be from one of the nodeshaving a link layer 1. When the central node receives such a message,the acknowledgment will be in the form of an SCMM, with an updated, ifnecessary, set of data. The SCMM is heard by all link layer 1 nodes, andto the extent that a change in the central node condition was included,all these link layer 1 nodes will make the necessary changes to theirrouting to accommodate the change, if necessary.

For instance, to optimize throughput in the link layered network andavoid excessive loss of messages, it is very important that thefrequency of the carrier radio signal be as close as possible to thenetwork frequency, as explained further below. Various local operationalfactors affect the transmitters frequency and from time to time thedeviation from the network frequency must be corrected. When the centralnode receives a message from one of its link layer 1 nodes, it comparesthe frequency to the central frequency of the network and the SCMM sentback includes the deviation from that standard frequency. If thedeviation is greater than a predetermined value, an algorithm, describedin more detail below, causes the local processor at the node receivingthe SCMM to readjust the broadcast frequency to the network's frequency.

It should be noted, that the SCMM is received not only by the node thatsent the message to which the SCMM is an acknowledgment, but by allnodes that are within the range of the node transmitting the SCMM.However, only the node that sent the original message acts oninformation relative to frequency deviation, other nodes that “hear”that SCMM do not act on that information.

Similarly, the SCMM contains data from the responding node indicatingthe strength of the signal it received by the node sending the originalsignal. If that signal is outside a given range of strength, analgorithm at the sending node, now receiving that SCMM, will then adjustthe signal strength for the next transmission to be within the desiredrange. Here too, the nodes in the system that receive that SCMM (whichis not directed to them), will not act on this signal strength data. Weterm these data, namely, “frequency deviation”, and “Received SignalStrength”, “Unique” SCMM data, in that only the node that sent a messageto which the SCMM is an acknowledgment can act on such data.

Since the link layered networks of the present invention are dynamic,contain nodes of various capacities and may change in time, the capacityof a node (the length of a packet transmitted) may change in time aswell. Such capacity is also included in the SCMM and treated as a“Unique” data.

On the other hand, each SCMM will include data that are “Universal”,namely, every node that receives that SCMM, whether or not it is thesender of the message that elicited the SCMM acknowledgment, may act onsuch data. Universal data include the time at the acknowledging node anda measure relating to the then current rate of packet processing, thatnode is engaged in (for instance in the form of a number designating thenumber of packets processed in the last 60 seconds). In some embodimentsof the invention, however, it is better to treat the rate of packetprocessing as “Unique” data acted upon only by the node instigating thesending of the SCMM, as is further described below.

It should be mentioned here that time synchronization within a linklayered network was already taught in '569 and '236, and in theembodiment of the present invention, such is simply adopted from thepresent inventor's prior work. Suffice to say that the inclusion of thetime at the acknowledging node in the SCMM allows the link layerednetwork to standardize and synchronize a universal time at all nodeswithin the network

The inclusion in the SCMM of the rate of packet processing at a givennode, allows now for geographical redistribution of radio traffic awayfrom nodes that are critical nodes. When the SCMM indicates that theacknowledging node has a rate of packet processing greater than apredetermined threshold, the node originating the message will select aroute avoiding the critical node that acknowledged last (with said SCMM)and may even increase its link layer level to do so as described in moredetails below.

There will be occasions, such as after power outages, or a rolling blackout, or even after intentional network shut down, when the network ispowered up simultaneously. In the prior art, the simultaneous poweringup or awakening of a link layered network encountered major difficultiesdue to the creation of excessive radio traffic as each node in thesystem attempts to reestablish and validate its routing lists. Underextreme conditions, particularly in high nodes density networks, suchnetwork awakening can take an inordinately long period of time to fullyreestablish all communication links and routing optimization. In thepresent invention, this problem is solved by stratifying the awakeningprocess and randomizing the awakening process at each link layer level.

Specifically, delay times are introduced post re-powering of thenetwork, or any specific node, before a node actively seeks toreestablish routing lists and thus communication links to the linklayered network, through a “discovery” message sent by the awakeningnode. The delay time before transmitting a discovery packet is longerthe higher the link layer level, n, of the node is. Furthermore, sincethere might be a very large number of nodes having the same link layer,in some embodiments of the invention, reestablishment of thecommunication links of nodes having the same link layer is alsostratified. This stratification is achieved by having said delay timerandomized between the nodes having the same link layer, within the linklayer level assigned delay time window, as further explained below.

It should be understood that an SCMM is sent in response to the receiptof a message, not just by the central node, but by any node receiving amessage from a neighboring node. Thus, any modification in theoptimization process creeps up the various links within the link layerednetwork until all nodes have updated their routing lists as well theirown various operational parameters, such as adjusting their broadcastfrequency, adjusting their signal strength, keeping their local internalclock in synchronism with the central node, and seeking alternateroutes, when message characteristics have changed for one reason oranother.

For clarity, it is easier to discuss two types of SCMM, we term theseSCMM(+) and SCMM(−). An SCMM(+) is one sent in response to a messagereceived from a node having a higher link layer (typically, a messageeventually destined to reach the central node), while SCMM(−) is an SCMMsent as an acknowledgment of receipt of a message from a node having alower link layer (thus a message destined to a subscriber deeper in thefield). Since the majority of this specification deals with SCMM(+), itshould be understood that in the following, SCMM will mean SCMM(+), andonly when discussing an SCMM sent in response to a message originatingat a node having a lower link layer, the terminology SCMM(−) will beused.

In one aspect the invention is a method of dynamically keepingoperational and optimized, without operator intervention, in response tochanges occurring at any node, a wireless link layered networkcomprising a plurality of transceivers at respective nodes which routecommunications from any node to a then central node of the network andwherein said communications are in a form of information packetstransmitted from one node to another. The method comprises the steps of:

(a) from each node successfully receiving an information packet,eliciting as an acknowledgment, a system control and modifying message(SCMM) containing optionally the following items of information:

(a1) a current time at the receiving node,

(a2) a received signal strength,

(a3) a packet length or capacity of the receiving node,

(a4) a most recent utilization rate of the receiving node,

(a5) a deviation from standard network frequency of the receivedinformation packet,

(a6) an identification of the receiving node,

(a7) an identification of the node eliciting the SCMM, and

(a8) a packet sequence identifier for the acknowledged informationpacket;

(b) determining whether the node originating the SCMM is from a linklayer level equal to or less than the link layer level of the nodeeliciting the SCMM; and

(c) where the node originating the SCMM has a link layer level equal toor less than the link layer level of the node eliciting the SCMM, at theeliciting node and in response to the SCMM, rerouting and/or adjustingfuture transmissions based at least upon some of the information items(a1-a6) contained in the SCMM.

The method can include:

at the node eliciting the SCMM:

(i) determining whether the node receiving the acknowledged informationpacket and from which the SCMM has been elicited has adequate capacityfor the acknowledged information packet;

(ii) if the node from which the SCMM has been elicited has insufficientcapacity, registering that capacity for other messages and routingfuture messages requiring the capacity of the acknowledged informationpacket through other nodes; and

(iii) if the node from which the SCMM has been elicited has sufficientcapacity, registering that capacity and continue to route futuremessages requiring the capacity of the acknowledged information packetthrough that node

The method can also include at the node eliciting said SCMM:

(i) determining whether the node from which the SCMM has been elicitedhas adequate received signal strength for the acknowledged informationpacket;

(ii) if the node from which the SCMM has been elicited has insufficientreceived signal strength, at the eliciting node, increasing power by anamount which will cause the received signal strength to be equal to anideal signal strength for other messages to be routed through that node;

(iii) if the node from which the SCMM has been elicited has greaterreceived signal strength than an ideal value at the eliciting node,decreasing power by an amount which will cause the received signalstrength to be equal to the ideal signal strength; and

(iv) registering a new power value for the node from which the SCMM hasbeen elicited.

The step (ii), the power can be increased to a maximum power availableat the node eliciting the SCMM.

In a feature of the invention the method further comprises from theutilization rate included in the SCMM, determining at the node elicitingthe SCMM whether the utilization of the node from which the SCMM hasbeen elicited is such that the node from which the SCMM has beenelicited should be used further and/or altering routing informationstored at least one of a plurality of nodes receiving the broadcast SCMMbased upon the degree of utilization incorporated in the SCMM.

From the utilization rate included in the SCMM, it can be determined atthe node eliciting the SCMM whether the utilization of the node fromwhich the SCMM has been elicited is such that the node from which theSCMM has been elicited should be used further and/or altering routinginformation stored in the node eliciting the SCMM should be altered.

It is possible from information in said SCMM as to a deviation fromstandard network frequency of the received information packet, to reducea broadcast frequency at the node eliciting the SCMM to equal an SCMMoriginating node frequency or increase the broadcast frequency at thenode eliciting the SCMM to equal the SCMM originating node frequency.

A new frequency can be stored at the node eliciting the SCMM in afrequency database thereof.

The method can further comprise:

comparing said current time information from the SCMM with a clock of anode receiving the SCMM; and

decreasing or increasing the time of the clock at each node receivingsaid SCMM to equal the time represented by said time information plusthe time to propagate the time signal to the respective node.

In another aspect the method of dynamically keeping operational andoptimized, without operator intervention, in response to changesoccurring at any node, a wireless link layered network comprising aplurality of transceivers at respective nodes which route communicationsfrom any node to a then central node of the network and wherein saidcommunications are in a form of information packets transmitted from onenode to another can comprise the steps of:

(a) broadcasting from each node successfully receiving an informationpacket, as an acknowledgment, a system control and modifying message(SCMM) containing at least the following items of information:

-   -   (a1) a current time at the receiving node, and    -   (a2) a most recent utilization rate of the receiving node,

(b) at any node capturing said SCMM, determining whether the nodeoriginating the SCMM is from a link layer level equal to or less thanthe link layer level of the node capturing the SCMM; and

(c) where the node originating the SCMM has a link layer level equal toor less than the link layer level of the node capturing the SCMM, inresponse to the SCMM carrying out required changes at all nodes of thenetwork capturing said SCMM based upon the information items (a1 and a2)contained in the SCMM.

The changes can include adjustment of local time at each of the nodescapturing said SOD! based upon the time information (a1). The change canalso include rerouting of information packets to other nodes than saidreceiving node when said receiving node has a utilization rate above apreset threshold.

The invention is also a method of preventing network oscillation in awireless link layered network comprising a plurality of transceivers atrespective nodes which route communications from any node to a thencentral node of the network and wherein said communications are in aform of information packets transmitted from one node to another, saidmethod comprising the steps of:

(a) from each node from which a message is to be sent to other nodes ofsaid network, attaching a token specific to each message sent;

(b) sending the messages with the tokens attached to other nodes of thenetwork; and

(c) rejecting for retransmission at each node any received messagecontaining the token specific to that node.

In its method aspects the invention includes a method of preventingnetwork congestion upon restart of a wireless link layered networkcomprising a plurality of transceivers at respective nodes which routecommunications from any node to a then central node of the network andwherein said communications are in a form of information packetstransmitted from one node to another, said method comprising stratifyingreestablishment of communication among said nodes whereby restart iseffected layer by layer, and within each link layer level, restart timeis randomized.

In an apparatus aspect the invention is a wireless link layered networkcomprising a plurality of transceivers at respective nodes which routecommunications from any node to a then central node of the network andwherein said communications are in a form of information packetstransmitted from one node to another, some of the nodes having a linklayer level less than the link layer level of others of said nodes, saidnodes being configured upon successfully receiving an informationpacket, to generate as an acknowledgment, a system control and modifyingmessage (SCMM) containing optionally the following items of information:

(a1) a current time at the receiving node,

(a2) a received signal strength,

(a3) a packet length or capacity of the receiving node,

(a4) a most recent utilization rate of the receiving node,

(a5) a deviation from standard network frequency of the receivedinformation packet,

(a6) an identification of the receiving node,

(a7) an identification of the node eliciting the SCMM, and

(a8) a packet sequence identifier for the acknowledged informationpacket,

each transmitting node determining whether the node originating the SCMMis from a link layer level equal to or less than the link layer level ofthe node eliciting the SCMM, and where the node originating the SCMM hasa link layer level equal to or less than the link layer level of thenode eliciting the SCMM, in response to the SCMM at the node elicitingthe SCMM, rerouting and/or adjusting future transmissions based at leastupon some of the information items (a1-a6) contained in the SCMM.

A wireless link layered network of the invention can comprise aplurality of transceivers at respective nodes which route communicationsfrom any node to a then central node of the network and wherein saidcommunications are in a form of information packets transmitted from onenode to another, said nodes being configured upon successful receipt ofan information packet, to generate as an acknowledgment, a systemcontrol and modifying message (SCMM) containing at least the followingitems of information:

-   -   (a1) a current time at the receiving node, and    -   (a2) a most recent utilization rate of the receiving node, and

upon determining whether the node originating the SCMM is from a linklayer level equal to or less than the link layer level of the nodeeliciting the SCMM, resetting a local time for each node receiving theSCMM where the node originating the SCMM has a link layer level equal toor less than the link layer level of the node eliciting the SCMM, inresponse to current time at the node originating the SCMM or reroutinginformation packets to other nodes in response to an excessiveutilization rate of the node originating the SCMM.

The wireless link layered network can comprise a plurality oftransceivers at respective nodes which route communications from anynode to a then central node of the network and wherein saidcommunications are in a form of information packets transmitted from onenode to another, in which the continuous retransmission of the samemessage in a sub set of the nodes is prevented, said prevention beingeffected by including in each information packet to be sent to othernodes of said network a token specific to the sending node and byrejecting for retransmission at each node any received messagecontaining the token specific to that node.

The invention includes a wireless link layered network, which inresponse to changes at any node, is dynamically and without theintervention of an operator kept operational, by promulgating into thenetwork information as to such changes via message acknowledging SCMM,and assuring that only the node eliciting such an SCMM uniquely actsupon said information, providing the SCMM originated from a node havinga link layer equal or lower than the eliciting node.

The invention also includes a wireless link layered network which inresponse to communication crowding in some of its communication path,dynamically and without the intervention of an operator reroutes messageto parts of the network that are less congested, said rerouting beingaffected by having all nodes capturing an SCMM from a node having highutilization rate exceeding a preset level, removing said SCMMoriginating node from their respective routing list, provided that thelink layer level of the node originating the SCMM is equal or lower thaneach respective node capturing said SCMM.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the inventionwill become more readily apparent from the following description,reference being made to the accompanying drawings in which:

FIG. 1 is a diagram for a general description of a link layered networkhaving a plurality of nodes having different capacities;

FIG. 2 is a block diagram of a typical subscriber unit (node);

FIG. 3 is a block diagram of a then designated central node;

FIG. 4 is a logic diagram of rerouting due to packet capacity changes;

FIG. 5 is a logic diagram providing adjustment to received signalstrength;

FIG. 6 is a logic diagram describing the process of calculating autilization factor;

FIG. 7 is a logic diagram of rerouting due to excessive utilization;

FIG. 8 is a logic diagram implementing system wide frequencystandardization;

FIG. 9 is a logic diagram implementing system wide time synchronization;

FIG. 10 is a logic diagram of loop formation prevention;

FIG. 11 is a logic diagram implementing stratified awakening of thenetwork; and

FIG. 12 is a diagram of an application of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic depiction of a link layered network, 1, havinga central node, 10, and a plurality of subscriber nodes, 11 and 12. Thesubscriber nodes 11 and 12 differ from each other, in that they may berespectively older and newer technologies, or attached to different typeof subscribers. It should be understood that a modern link layerednetwork may include more than two such classes of nodes, and that FIG. 1shows only two such classes only for simplification purposes. FIG. 1also depicts a topological, geographical or terrain type barrier, 13,that might run through the network's space. Such a terrain feature canprevent direct communications of some of the nodes to the central nodeand creating in the process nodes that have become critical, in that toomuch traffic would normally be directed through them. It should beunderstood that a node can become critical not only due to terrainconstraint, but also because some nodes, due to technologicalsuperiority, or superior antenna placement, get included in thepreferred routing list of more of the nodes in the network.

In FIG. 2, is shown a typical subscriber node, 11 or 12. The nodeinterfaces with the local environment through inputs and outputs, 14.Inputs may be, but are not limited to, alarm conditions, results ofmeter readings, data stream related to credit card transactions, variousautomated inventory readings (such as in networked vending machines)etc. Outputs might be various commands, such as credit card transactionauthorization, turning on and off various devices (particularly inremotely controlled processes and electrical load optimization schemes),various system resetting etc.

The interface of the subscriber node to the RF network is through anantenna, 15, connected to a transceiver module, 16 (which of coursecomprises of a receiver and transmitter module). Signals received at, ortransmitted from the node, are processed in a central processing unit,CPU, 17. Not shown for simplicity are associated signal processing andconditioning elements between the CPU and the transceiver. Each node hasboth volatile memory 18, and non volatile memory 19. Typically, the nonvolatile memory will contain various programs related to the nodeoperation and its control in general, programs that execute routingalgorithms as well as a number of preferred routing lists. The volatilememory is used to store received and ready to be sent or repeatedpackets as well as most current routing lists.

The routing list contains not only the nodes through which packets areto be repeated, or to which new packets need to be sent, but also thecapacity of the node, namely the length of the packets capable of beingtransmitted through the node, the utilization rate of the node as wellas the power level to be used in transmitting packets to variousneighboring nodes. It should be understood that the power level oftransmission is unique to the unique neighboring node a packet may beaddressed to.

It should be understood that different kind of nodes may have differentcapacities in said memories, thus the length of packets transmittable bydifferent types of nodes could and is different in such a network.

Each node is powered by a power supply unit and has its own back upbattery (20 and 21 respectively). In some embodiments of the networks ofthe present invention, the power supply is simply a battery, or it maybe powered by the AC mains with no battery, or it may have both AC mainsand a battery, (in some cases the battery is rechargeable from solarpanels, or AC mains). The nature of the power source in a given nodeimposes limitations on the ability of these nodes to activelyparticipate in the link layered network packet repeating features, andis taken into account when the network is forced to reconfigure itselfdynamically, due to changes in the network's conditions or the conditionof the node.

In FIG. 3, the central node 10, has a similar interface with thenetwork, consisting of an antenna 22, and a transceiver 23. Theinterface to any central command center, data collection center, creditauthorization type of system etc, is conducted through an input/outputmodule 24 and a variety of communication means (25 to 32). Apart of theinterface with a “central command center” (or equivalent), the centralnode is quite similar to subscriber's nodes, in that it has a CPU 33,volatile and non volatile memory 34 and 35 respectively, as well as apower supply, 36 and back up battery 37.

While typically, the communication means between the central node (thecentral node has by definition a link layer of 0) and wherever the dataare used or various network commands are issued, are relatively fixed.However, from time to time, there is a need to change such a link. Forinstance, initially, said communication link could be via a land linetelephone 29, with a relatively high capacity, but an unanticipatedfailure of such a connection may force the system to “fall back,” onanother means of communication, for instance, an independent radio link(typically at a different frequency than the frequency used by the linklayered network) which has much smaller capacity.

It should be understood that capacity changes in other nodes, not onlythe central node, could occur as well in a dynamic system. It istherefore necessary to adjust routing to cope with such changes incapacity. In the instant invention, this is achieved by configuring thetraditional acknowledgment (Ack) message in a unique manner as a “SystemControl and Modifying Message”, or an SCMM. Specifically, the SCMM.contains within it the capacity of the acknowledging node.

In FIG. 4, we show an algorithm designed to assure that the routing ofmessages always account for the capacity of the nodes involved in aspecific route. Typically, a node will be sending a data packet at 40,and then wait to receive an acknowledgment in the form of an SCMM at 41.Once the SCMM was received at 42, the SCMM is parsed at 43 and the linklayer level of the acknowledging node, the one that responded with theSCMM, is read at decision box 44.

If the SCMM is an SCMM(−), the link layer of the node sending the SCMMis greater than the receiving node link layer, thus “NO” at decision box44 is selected , no change is implemented, at 45, and the system goesback to be ready to send the next packet on its list at 40. This assuresthat capacity changes indications flow from lower link layers to higherlink layers in the system, thus spreading out into the network theinformation about a new capacity requirement, or special routes forspecial capacity packets. This feature of the algorithm, assuresdirectionality of changes from the central node to all nodes in thenetwork, so that capacity information from an SCMM(−) does not causechanges in nodes of lower link layers.

Referring back to decision box 44, if the link layer of theacknowledging node which sent the last SCMM is equal or lower than thelink layer level at the receiving node, “YES” is selected at decisionbox 44. At box 46, the capacity data are retrieved from the parsed SCMM,read at 47 and at decision box 48 the capacity of the node sending theSCMM is compared to the packet capacity at the receiving node. If saidcapacity is within the boundaries of the range of values that thereceiving node uses for transmitting its own packets, “YES” is selectedat decision box 48, and no action is taken at 45, and the node isreadied to transmit the next packet on its list at 40. If, however, atdecision box 48 it is determined that the capacity of the acknowledgingnode, the node replying with the SCMM, is outside said boundaries, “NO”is selected. It should be understood, that due to the dynamic nature ofthe link layer network, changes in the capacity of nodes (including thecentral node) can occur at any time. This can be the result of additionsof new nodes to the system, changes in the central node or failure ofsome existing lower link layer nodes. The changes can be eitherincreases or decreases in node capacity. The test at decision box 48simply ascertains that the capacity of lower link layer nodes has notchanged (“Yes” in box 48) or changed (“NO” in box 48). If “no” isselected, at decision box 49, the capacity of the node originating theSCMM is compared to the local node's capacity. If said capacity isgreater than the local capacity, “Greater than” is selected. The valuechosen at 48 is selected so that no oscillation will be caused by smallchanges in said capacity.

At 50, the origin of the SCMM is noted in the local routing data base,marking the node sending said SCMM at the top of the routing list forpackets of that capacity or smaller (if it was not already the preferrednode), and storing this capacity information for that node in the localnode routing list at 51.

However, if at decision box 49, “Less than” is selected, at 52, theorigin of that SCMM is noted as one that cannot be used to route packets(of that capacity), and at 52, that information is updated by removingthe origin of the SCMM from the local routing list for the statedcapacity. The last box 53, is equivalent to the box 40, where the systemis now ready to send the next data packet, this time, with a new routinglist.

Thus, by implementing the algorithm described in FIG. 4, the local nodesknow at all times what is the maximum capacity packets that can betransmitted through any of its neighboring nodes.

It should be appreciated that node packet capacity in a link layerednetwork may change in time not only due to changes in the type ofcommunication the central node might have with a “central command”station, as mentioned above. Under some circumstances, some criticalnodes may drop from the network or come back on, and since it is alwaysdesired to send packets through the network at the highest capacitypossible, such changes are propagated in the network by using thealgorithm shown in FIG. 4 on each SCMM. It should also be appreciatedthat such changes in capacity are always driven upward from lower linklayer nodes to higher link layer nodes. In that respect, the linklayered network is not truly a mesh network but a hierarchy tree networkwith a specific directionality of implementation of route updates andmodifications.

As mentioned above, the routing list must also contain for each node thethen best power level at which it will transmit a packet to a targetnode. If the power is too low, packet loss (complete or partial) mayresult. If the power level is too high, congestion of the airwave withunnecessary traffic will result.

In FIG. 5, is shown a flow diagram of the algorithm used to keep eachnode at the proper power level for optimizing communications in the linklayered network of the present invention. Specifically, at 60, a datapacket is sent, and at 61, the node is waiting for an acknowledgment inthe form of an SCMM from the node to which the packet was sent. The nodethen receives the SCMM at 62 and parse said SCMM at 63.

As before, to assure that modification in routing conditions is onlyconducted from lower link layers to higher link layers, at decision box64, SCMM(−) are discarded by determining if the SCMM is from a nodehaving a link layer equal to or lower than that of the local node. Ifthe SCMM is from a node having a higher link layer, “NO” is selected atdecision box 64, and at 65, nothing is done and the node is ready tosend the next packet at 60.

However, if at decision box 64, “YES”, is selected, namely the SCMM isfrom a node having either a lower or equal link layer than that of thelocal node. At 66, the Received Signal Strength Indicator (RSSI) isretrieved from the incoming SCMM and read at 67. At decision box 68, itis determined if the RSSI is within the boundaries of operational rangeacceptable.

It should be understood, here, that not every deviation of the RSSI fromthe standard is acted upon at the local node, only when the RSSIdeviation exceeds certain values from the desired set value,modification of the signal strength will be implemented. This as inearlier discussions prevents oscillation of the transmitter power levelsand potential link layer structure of the network. Thus, if the RSSI isacceptable, “YES” is selected at decision box, 68, and at 65, the nodeis being readied for the next data packet transmission at 60. If,however, the RSSI is outside acceptable boundaries, at decision box, 68,“NO” is selected and at decision box 69, it is determined if the RSSI isgreater than or less than said ideal RSSI value. If the RSSI is greaterthan the desired RSSI, “Greater Than” is selected and at box 70, thepower setting at the node is lowered by an amount that will bring theRSSI as close as feasible (typically, in most networks, power incrementsand reductions are not continuous) to the ideal RSSI.

The new power level setting is stored in the routing list at 71 (for therouting list directed at the node that sent the last SCMM), and the nodeis returned at 72 to box 60, readying the node for the next packettransmission. When the RSSI is less than the ideal RSSI, “Less Than” isselected at decision box 69, and at box 73, the power setting at thenode is increased by an amount that will bring the RSSI, as close asfeasible, to the ideal RSSI value unless the node is at the maximumpower where the receiving node should be noted as having reducedtransmission capacity in the routing table. The new power setting isthen stored as part of the routing list at 71, and at 72, the node isreturned to 60, readying it to send the next packet transmission.

Apart from the capacity of a target node first on the routing list, andthe optimal power setting to reach such a node, it is important thatsuch a target node will not be too busy transmitting packets from othernodes in the link layered network, nor is it desirable to use as arepeating node, a node that might have local technical problems.Therefore, in the practice of the present invention, a unique parameterwhich we have termed “node utilization factor” is designed and. used indetermining whether a node would be used or not in a routing list.

The algorithm describing how the utilization factor is derived is shownin FIG. 6. Specifically, at 80, a data packet is received and atdecision box 81, it is determined if the packet was received correctly.If the node had reception problems with said packet, “NO” is selectedand a NACK (no Acknowledgment) packet is prepared at 82 and sent at 83.If the packet was received correctly, “YES” is selected at decision box81 and at 84, the start of an SCMM formation is executed (it includesamongst other things, “Capacity Notification” as in FIG. 4,determination of the RSSI as in FIG. 5, Frequency Adjustments as in FIG.8 and Time Synchronization as in FIG. 9).

The utilization factor which is calculated at 90, consists of three mainelements. The most important is the historical percentage of the totalelapsed time that the local transmitter is busy transmitting packets andis calculated at 87. This historical time frame is arbitrary, in someembodiments of the invention, that percentage is being averaged over theperiod from the last “power-up” of the node. In most cases, a rationalmoving average over a period of few hours is a better value for thepercentage of the time the transmitter at the node is on. In very activenetworks, shorter time intervals are used as moving averages todetermine said percentage.

Let's reconsider FIG. 1 and concentrate on the nodes of the type “12”.As shown in that figure, the central node, 10, is positioned south of aridge (or it could be another type of geographical obstruction) with thenode 101 serving as a link between nodes in the northwestern quadrant ofthe system and the central node. Typically, node 101 will be in therouting list of nodes 102, 103, 104, 105 and 106, and relays messages tothe central node, 10, either directly, or through node 109. That maycause node 101 to become over utilized, and may even cause clogging ofthe network at that location. In the practice of the present invention,such overburdening of a repeater node is avoided by including in theSCMM from node 101, a utilization factor, reflecting the rate ofutilization of that node. If the rate exceeds a preset value, traffic,for instance, from nodes 105 and 106, may be rerouted through nodes 107,108 and 110 to the central node, thus lowering the load on node 101.

The result will be de-optimization of the number of hops from 105 and106 to the central node, yet preserving the network overall optimalutilization of the available RF spectrum in that geography. Note thattypically, node 109 will have a link layer,1, 101 a link layer 2, andnodes 102, 103 and 104, which will still be using node 101, as arepeater to the central node, have a link layer 3 (It should be notedthat if node 101 communicates directly with the central node, 10, itslink layer level will be 1, and the link layer level of nodes 102, 103and 104 will be 2). Nodes 105 and 106 would also have a link layer of 3if they used node 101 as their route to the central node, however, when101 is already overburdened, node 106 might have a link layer of 4(going through 107, 108 and either 110 or 109), and node 105 might evenhave a link layer 5, if it cannot communicate directly to 107 and needto use node 106 as an intermediate repeater.

A typical rate of packet processing at a node that would instigatechange in routing, would be latency in the range of 0.333 to 0.666.Namely, if a node is busy repeating packets between ⅓ and ⅔ of the time,it should not be included in additional nodes routing list and marked asa high utilization rate node. To ascertain that a node is indeed a highquality node to be used in the retransmission of packets from nodeshaving higher link layers, it is important that other characteristics ofthe node be optimal. Thus, if the node in question may have powerlimitations, for instance if powered from a battery or another limitedpower source (such a solar cell powered battery system), suchlimitations become part of the utilization factor of that node. Suchpotential power limitation is recorded at 86 and is used at 90 tocalculate the eventual “Utilization Factor”. Similarly, if the nodesmight have any hardware problems or local events that could interferewith its ability to serve as a repeater, such is noted at 88 and used at90 as well to calculate the eventual Utilization Factor.

The end value of the Utilization Factor, is typically the arithmetic sumof the utilization rate determined at 87, the available power determinedat 86 and the occurrence of hardware problems or special local eventsdetermined at 88, as well as the native capability of the nodes hardwareas defined in 85. In order to ascertain that local failure of either thepower, or major local hardware problems, do not interfere with theability of the network to keep operational, the input from unacceptablelevels of node functionality determined at 86 and 88 is set usually ataround half the threshold, U (between 0.333 and 0.666) for theUtilization Factor. This result in that node being taken off the routinglist long before the utilization Factor alone causes such a rerouting tooccur, assuring the continuous readjustment and optimization of routingin the link layer network at all times.

Once a node has attached to each SCMM its own Utilization Factor, inFIG. 6, at box 91, and the SCMM is transmitted at box 92, the node thatelicited the SCMM can determine if that node is to be used in furtherfuture repeats of packets and include said note in its routing list. Insome embodiments of the present invention, the “utilization Factor” is a“unique” parameter, namely, only the node that elicited the SCMM willreact in the event that the utilization factor exceeded thepredetermined threshold, U. In other embodiments of the invention, theUtilization Factor is considered a “universal” parameter, and all nodesthat receive the SCMM reacts to an excessive utilization factor.

This is done as described in FIG. 7, which for simplicity presents boththe embodiment in which the Utilization Factor is treated as a uniqueparameter and the embodiment where the utilization factor is treated asa universal parameter. Specifically, at box 120, a data packet was sent,or the node simply listens to the network radio traffic. An SCMMgenerated at 92 is awaited for and received at 121, received at 122 andparsed at 123. At decision box, 124, it is, once more, ascertained thatthe SCMM is not an SCMM(−), thus has come from a node having a linklayer lower than the local node, if the SCMM is from a node with linklayer greater than the local node, “NO” is selected, nothing is done at125 and the node is readied to send another packet, or listen to thenetwork at 120.

If however, the node from which the SCMM was sent has a link layer equalor less than the local node, then “YES” is selected at box 124. At box126, the utilization factor is removed from the SCMM and read at box127. up to this point, the algorithm implementing the utilization factortest is the same in embodiments of the invention that consider theutilization factor a unique or a universal parameter. If one wants toimplement the utilization parameter as a unique parameter, namely, onlythe node eliciting the SCMM response is to act on the then current valueof the utilization factor, the branch denoted 128, is taken, anddecision boxes 133 and 134, simply do not exist in that embodiment. Atdecision box 129, the utilization factor from the incoming SCMM iscompared to a fixed threshold value “U” (typically between 0.333 and0.666), if it is less than “U”, “YES” is selected at box 129, and goingthrough 125 (do nothing), the node is readied to transmit the nextpacket and no change in its routing list is made.

If, however, at decision box 129, “NO” is selected, namely theutilization factor logged onto the SCMM is greater than “U”, then at box130, the origin of the SCMM is removed from the local node's routinglist, and the routing list is resorted at 131. The new routing list isnow stored at 132, and at 125, the node is readied to send the nextpacket.

As mentioned above, in some embodiments of the invention, theutilization factor contained in the SCMM is treated as “unique” data,namely, only the node that sent the packet to which the SCMM is anacknowledgment acts on the utilization factor received. This is toassure that not all nodes that use the repeater that sent the SCMM, actsimultaneously to remove that node (for instance, node 101 in FIG. 1).In FIG. 1, at least five nodes will receive (or “hear”) an SCMM from101, but only one node at a time should remove 101 from its routing listif the utilization factor exceeds “U”. If all the nodes (102, 103, 104,105 and 106) that can hear the SCMM change their routing listsimultaneously, suddenly, 101 will no longer be “over utilized” and thenetwork may be thrown into unnecessary oscillations, in the process ofseeking new routing lists.

In other embodiments of the invention, the utilization factor is treatedas “universal” data, namely, all nodes receiving that SCMM, whether ornot the SCMM is in response to their own sent packet, reacts to removethe node having an excessively high utilization rate from their routinglist. The decision if the utilization factor is “universal” data or a“unique” data is determined by the nature of the network. Typically,when it is desired to make the utilization factor “Universal” data, twoadditional decision boxes are used, 133 and 134 as shown in FIG. 7. Insuch an embodiment, the goal is to remove from the routing lists of allthe nodes that receive the SCMM, whether or not such nodes elicited saidSCMM, a node that has become, not just over utilized, but which alsosuffer from other problems, for instance, power limitations, or localhardware failures. Thus, in the embodiment of the invention where theutilization factor is universal data, branch 128 does not exist, andinstead, after reading the utilization factor from the SCMM at 127, theprogram goes to decision box 133 where it is determined whether the SCMMwas elicited by the local node (Ack to our packet?) or not. If the SCMMwas elicited by the local node, “YES” is selected at decision box 133,and the data are treated as if the utilization factor is unique data(through decision box 129 as described above).

If at decision box 133, it is determined that the SCMM was not elicitedby the local node, “NO” is selected, and at decision box 134, theutilization factor is compared to a threshold value αU, where α istypically greater than 1. If the utilization factor is less than the newand higher threshold value αU, no problems are “considered” encounteredwith that node, and thus the system returns to 125, “do nothing”, andthen back the listening to the network at 120. It should be noted thatfor nodes that did not elicit the SCMM, even if the utilization factorexceeded the threshold value, U, no action is taken. This, since thenode that elicited the SCMM will remove the origin of the SCMM from itsrouting list, and that might be sufficient to reduce the utilizationfactor of that node below the threshold in subsequent time intervals. Ifthe utilization factor of the SCMM origin is not reduced sufficiently,the next node eliciting an SCMM from that same SCMM origin will causefurther reduction in its utilization rate, until the utilization ratedeclined under the threshold value U.

In this manner, when a situation arises that a critical node hasdeteriorated markedly, resulting in a very high utilization factor,greater than the normal threshold value U (typically due to hardwareproblems or power problems), no delays in reconstituting the link layernetwork occur and immediate reaction of the network is obtained when allnodes that were using the, now faulty, node in their routing list, seekalternate routes.

There is an additional parameter that can impact efficiency as well asthe optimal operation of a link layered network, particularly when sucha network includes older technology nodes. With time, a transmitter'sfrequency, which is derived from a quartz crystal, can slowly drift, andwhen the frequency increases or decreases beyond specific limits, it canactually cause the transmitter to broadcast outside the allowed band(allowed by the FCC, or as it is commonly known the “occupied frequencymask”).

Furthermore, the farther the frequency is from the central frequency ofthe network, the more bit losses and even packet losses occurs. It istherefore important to maintain the frequency used to transmit packetsat each node of the link layered network, as close to the system or thecentral node's frequency as possible. Since none of the subscriber nodesare usually equipped with accurate frequency standards, the only way toassure that frequency drifts in the system do not reach excessive levelsthat interfere with the system operation, is the comparison at each nodeof its frequency with that of lower link level nodes. That process aswell is carried out via the SCMM.

Specifically, in FIG. 8 is shown the flow diagram and algorithm throughwhich frequency standardization is carried out. As before, with thecapacity utilization, signal strength and utilization rate, at 140, apacket is sent and at 141, the node awaits an SCMM. At 142, the SCMM isreceived and parsed at 143.

At decision box 144, it is ascertained that the SCMM is from a linklayer equal to or less than the local node. If the origin of the SCMMhas a higher link layer, the SCMM is a SCMM (−) and “NO” is selected at144, and at 145, nothing is done and the node is readied to transmit thenext message at 140. This, as before, with capacity, signal strength andutilization rate, assures that all changes in frequency are promulgatedthrough the network from lower link layers to higher link layers. If thelink layer of the SCMM origin is less or equal to that of the receivingnode, “YES” is selected at 144, and at 146, the frequency data of theSCMM originating node are removed and read at 147.

At decision box, 148, the local frequency is compared to the originatingnode's frequency. If the local frequency is very close to theoriginating node frequency and thus no change is necessary, “YES” isselected at 148. “YES” is also selected if the difference in frequencyis extremely high, and outside the allowed RF band for that frequency,and in essence no change is either feasible or allowable. That casewill, in most situations, be due to a major hardware failure occurringat the node, necessitating shutting down the node and servicing it. Thusat decision box 149, if the frequency at the local node is outside theallowed RF band, “YES” is selected, and the node is directed to shutdown at 150. If the frequency is not outside the allowed RF band, thenit must be very close to the SCMM originating node's frequency, “NO” isselected at decision box 149, going to 145, where “do nothing” is 15implemented and the node is readied at 140 for the next packettransmission.

If at decision box 148, it was determined that the frequency of the nodeoriginating the SCMM is different enough from the local node'sfrequency, but the difference is not so great that the local node needto be shut down, “NO” is selected. At decision box 151, it is thendetermined if the frequency of the originating node is “Greater than” or“Less than” the frequency of the SCMM's originating node. If the SCMMnode's frequency is greater than the local node's frequency, “Greaterthan” is selected and at box 152, the frequency of the local node isincreased to equal the frequency at the SCMM originating frequency. Thenew frequency is now stored in the local node frequency data base(essentially in the form of a multiplier or a factor of the localcrystal frequency) at 153, and at 154, the node is readied to send thenext data packet.

If the SCMM node's frequency is smaller than the local node's frequency,“Less than” is selected and at box 155, the frequency of the local nodeis reduced to equal the frequency at the SCMM originating frequency, andas before at 153, the new frequency is stored and at 154 the node isreadied for the next transmission.

Since there are a number of system commands that are executed at thevarious subscriber nodes at predetermined time intervals, or specificcommands that are broadcast to the network for execution at futuretimes, it is important that all nodes in the link layered network havetheir local clocks synchronized with the clock at the central node.

The SCMM of the instant invention in conjunction with the algorithmdescribed in FIG. 9 provide for such time synchronization. Since thetime is a “Universal” parameter, all nodes that “hear” an SCMM willcheck their clock against the clock at the node of origin of the SCMM,even if the nodes did not send a packet instigating the SCMMacknowledgment. Specifically, in FIG. 9, at 160, the node either send apacket or is listening to the network radio traffic to capture an SCMMwhich is not necessarily an acknowledgment to its own message. At 161and 162, the SCMM is waited for and received and parsed at 163.

It is necessary, as with other parameters discussed above, to promulgatethe “right time” from lower link nodes, or even from the central nodetoward the extremities of the network having higher link layers, thus atdecision box 164, we eliminate SCMM(−) that are “heard” at the node, bychecking if the SCMM packet is from a node having a link layer less orequal to the local node. If “NO” is selected, the SCMM is from a higherlink layer node and thus at 165, nothing is done, no change in the localclock is implemented and the node is returned to 160. If “YES” isselected at decision box 164, the time data are removed from the parsedSCMM at 166 and read at 167.

At decision box 168, the time data from the SCMM is compared to thelocal nodes' time. If the value is within predetermined boundaries whichdo not require any change in the local clock, “YES” is selected atdecision box 169, and at 165 “do nothing” is implemented and the systemis readied for the next transmission at 160. By allowing for definedvariations in the clocks of all the nodes in the network we preventoscillation of each node's clock.

If, however, the value of the time data read from the SCMM is outsidesaid boundaries, “NO” is selected and at decision box 169, it isdetermined if the SCMM time stamp is greater or smaller than the localclock's time. If the SCMM time stamp is greater than the local time,“Greater than” is selected, if lower, than “Less than” is selected.

When “Greater than” was selected at box 169, at 170, the local time isincreased to match the time read from the SCMM, plus a time interval,which is the time of propagation from the SCMM's originating node to thelocal node. The new time is now stored at the local node at 171, and at172, the system is readied (160) to send the next packet, or listen tothe network radio traffic.

The propagation time may be a set constant, it may be a set constantthat varies per link layer, or it may be the actual time the packet tookto reach a node. This actual time would be included in the SCMM packet.

When “Less than” is selected at box 169, at box 173, the local time isdecreased to match the time read from the SCMM, plus as before a time ofpropagation. Here as well, the new time is now stored at the local node171 and the system is readied at 172 for the next packet transmission,or listen to the network radio traffic.

Following the algorithm described in FIG. 9, assures that at all time,the local node, even if it has not sent a message out for a long time,has in its clock a time synchronized with the rest of the link layerednetwork.

Under some circumstances, particularly, when a critical node is lost anda group of subscriber nodes is temporarily isolated from communicationwith the central node, a link layered network will have a tendency to“bloom.” The term “blooming” is used for situations when the lack ofcompletion of a successful transmission of a packet from a remotesubscriber to the central node causes that group of nodes to send alarge number messages within the group. This is done automatically, inan effort to reestablish communications with the central node, and inthe process, each node involved keeps raising its own link layer, astaught in '569, in a futile attempt to reestablish communications. Inessence a loop is created in which the link layer levels of some or allthe nodes in that isolated group keeps increasing, and messages thatwere sent by a node return back to it, with no way found to the centralnode. Since such an event creates a lot of excessive traffic, it isimportant to rapidly filter out such repeated messages, until the routeto the central node is reestablished or an alternate route isestablished.

FIG. 10 describes an algorithm designed to assure that looping and theresulting blooming of link layers is not allowed to continue.Specifically, at the “Start”, 180, the node listens to the network radiotraffic, and as described in '569 and '236, determines if a packet isaddressed to the local node. In '569 when a local node queued a packetfor retransmission, an ignore flag was set (typically the ignore flagexpires after a preset time, about 3 minutes). Packets not addressed tothe local node are disregarded and at decision box 181, and 182, thepacket received is identified by its sequential number, or packet ID,and by its origin.

If the local node does not find in its recent list of packets sent anequal sequential number or ID number, the packet is not involved in aloop and “NO” is selected at 181. At decision box 183, the nodedetermines if the received packet is the last one on the transmissionlist Tx.

If at decision box 183, it is determined that the packet is the last onTx, the test for looping or the filtering test is ended, the packet isacknowledged with an SCMM and the packet is transmitted to the next nodeat 184. If there are other packets queued ahead, the node gets back tothe start of the filtering process.

If at decision box 181, “YES” was selected, namely a recent packet withthe same sequential number was recently handled at the local node, atdecision box 182, the node checks if the origin of the packet was alsoequal to a prior packet having the same sequential number. If “NO” isselected, at 183 the packet is either transmitted (if it is the last onTx and an SCMM is also transmitted at 184) or the system wait until thepacket reaches the top of Tx.

If both the sequential number of the packet and the origin of the packetare equal to those of a prior packet, we still try to “salvage” thesituation, if the packet was a “broadcast,” namely, a packet that needto be transmitted “at any cost,” including the danger of networkblooming. Thus at decision box 185, if the test “Is it our packet”fails, “NO” is selected,

Because it is desired to treat “Broadcast Packets”, which usuallycontain important commands to all the nodes, or at least a largesubgroup of all the nodes, in the link layered network, at decision box186, the query “Is the packet a broadcast” is posed, to see if thepacket is a “broadcast” or not. It the packet is indeed a “Broadcast”,“YES” is selected at 186, and despite the obvious problems identifiedbefore, the packet is still queued at 183 and if it is the last packeton Tx, for acknowledgment and retransmission at 184. If the packet isnot the last on Tx′ it goes back to “start” (180), until it becomes thetop of Tx.

If the packet is not a broadcast, it must be a packet from another node,for retransmission, that somehow has come back after it wasretransmitted earlier and thus possibly a nascent loop is formed. Such arepeated packet is treated like a repeated packet generated locally. Ifat 185, it is determined that the packet originated at the local node,and is thus definitely a possible looping process is in progress, “YES”is selected at 185, which may eventually lead to acknowledgment (at188), but with no retransmission.

At decision box 187, repeated packets, whether originating locally orelsewhere, as long as they are not “Broadcast Packets”, and thus simpledata packets, we check if the “ignore flag” (set earlier on the firsttransmission of that packet) is still on. If the “ignore flag” is stillon, the packet is acknowledged with an SCMM, but not retransmitted at188, since that packet, a very short while ago, was sent from the localnode and has returned through a looping process. By not re-transmittingthe package, the loop is interrupted, however, the packet is lost. Yet,the network is prevented from going into a lengthy set of packettransmissions that occupy the airwave and prevent reconstitution later,of the appropriate routings for the various nodes.

If the “ignore flag” is no longer set, it means that it has been sometime (at least three minutes) since the packet was transmitted, “NO” isselected at decision box 187, and decision box 189, we check if the linklayer attached to the message (from the last re-transmitting node) isthe same as the last time the packet was handled in the local node. Ifit the same, no blooming, or no increase in link layers of neighboringnodes has occurred, thus most likely, the repeat was simply accidental.At 189, “YES” is selected, and another attempt to retransmit the packetis conducted at 183, after assuring the packet is at the top of thetransmitting list, Tx. If, however, it is found at 189 that the linklayer is different (and it has to be greater than last time, due toblooming), and the packet must have returned after some nodes attemptedto reestablish connectivity to the central node by incrementing theirlink layer levels, “NO” is selected at 189. That will causeacknowledgment with an SCMM of the receipt of the packet at 188, but notransmission of the packet, thus interrupting the blooming process.

In this manner, temporary disconnection or failure of some criticalnodes in the system, will not result in the incessant transmission ofmessages within the system in a futile attempt to reestablishconnectivity. Once the fault in the system is taken care of,reestablishment of various routing lists from the last routing lists ateach node can be accomplished, without the process of bloomingcorrupting the routing lists at a large number of nodes.

As mentioned earlier, there are occasions when a link layered networksuffers total or partial power failures leading to shut down of a largenumber, if not all the nodes in the network. In the prior art, uponpower restoration, all nodes would send out a “Discovery” packet iftheir routing lists were no longer valid, and often that would causeflooding of radio space with the packets and acknowledgments from alarge number of nodes, making it very difficult to reestablish arational routing lists at all nodes in the network. In order to overcomethat problem, a stratified awakening with priorities is established inthe present invention, that assures the gradual wakeup of the network,without crowding of the airwaves with unnecessary traffic.

FIG. 11 shows an algorithm that provides for such stratified awakeningof the network. At 190, a subscriber is powered up, after a presumedblack out, or a rolling black out. At decision box 191, it is determinedwhether the node has a valid link layer. The node might be a “new node”and thus not have a link layer, it may have also lost its routing listdue to the previous unique event that shut down the network. It shouldbe understood, that most nodes will still have a valid routing list intheir memory. However, if it is determined at 191, that the node doesnot have a valid link layer, “NO” is selected at 191 and a “discoverypacket” is transmitted at 192. The nature of the “discovery packet” wasdescribed in detail in '569 and '236 of the present inventor, and saiddescription is incorporated herein.

If at decision box 191, it is determined that the node has a valid linklayer (and thus, of course, a valid routing list), and at box 193, atimer flag is set for a delay of nt₁r, where n is the node's link layerlevel, t₁ is a predetermined time interval (between 30 seconds to 120seconds, typically we use 65 seconds), and r is a random number,typically between 0.5 to 1.5, but can be well outside of that range inunique link layered network. The delay time nt₁r creates temporalwindows in which nodes having the same link layer reestablish theirrouting lists. The process therefore stratifies the awakening of thenetwork, and spread it in time from lower link layers to higher linklayer. The random number factor (typically with up to two decimalpoints, but with networks having thousands of nodes more decimal pointscan be used to provide for a more refined “staggering” of the wake upradio traffic.)

At decision box 194, during the delay period of nt₁r the node continuesto listen to the radio traffic in the network, and if it received anySCMM, which is congruent with its then existing routing list, it goesback to box 195 to listen to the network. if it is not congruent withits routing list, the list is modified according to principles taught in'569 and the node goes to listen to the network at 195. That node is nowback in the network.

If, however, no SCMM is received, at box 194 “NO” is selected and at box196, it is determined if the set delay time nt₁r has lapsed or not. Ifthe delay time has not been waited out yet, we go back to 193 to waitout the set delay time, and repeat the process, until the delay timent₁r has lapsed. Once the delay time nt₁r has lapsed, “YES” is selectedat decision box 196, and at box 192, a discovery packet is composed andtransmitted. The system now sets up a second fixed delay time, t₂(typically around 30 seconds) and at decision box 197, we check if anySCMM has been received. If such an SCMM was received at the node, “YES”is selected at 197, and the node is now with an effective routing listand goes back to listen to the network at 195. If, however, no SCMM wasreceived at 197, “NO” is selected and at decision box 198, we check ifthe delay time t₂ has lapsed or not. If it has not, we go into a timingloop at box 199 which in essence waits until the period t₂ from thesending of the discovery packet at 192 lapsed or not. Once that delaytime lapsed, “YES” is selected at 198. That means that the lastdiscovery packet elicited no SCMM response, and there is therefore aneed to send a new discovery packet at 192, until an SCMM is finallyreceived and the local node is integrated into the link layered network.It should be noted that in order to validate the link layer found in box191, any SCMM, whether from a node up or down the hierarchy of the linklayer network will suffice. That is done to assure that the number ofdiscovery packets transmitted upon a network awakening is minimized.

It should be obvious that while the awakening algorithm was designed tominimize radio traffic post major failure or restarts of the network,the same algorithm is used at any node if it is either a new node, or anode that lost power on its own, without the whole or major parts of thenetwork failing. In essence, a node does not “know” if the whole networkis down or not, and thus that algorithm is used whenever a node isre-powered.

EXAMPLE

One example where a link layered network of the present invention isparticularly useful, is in a city setting, where a large number ofbuildings contain each a plurality of systems that need to be monitored.In some instances, the monitoring is localized at each building, but inmany cases it is also desired to have such monitoring and controlfunction localized and away from each building. There are alsoembodiments where such monitoring and control is both local at eachbuilding or some of the buildings and remote from a central controlstation.

Thus in FIG. 12 there is shown a link layered network 200, having onecentral node 201, and a plurality of nodes (202 to 207), each oneassociated with a unique building. Data monitored are varied and includeamongst others, metering of power use and electric loading, metering ofnatural gas use and water use, and these not only for the whole buildingbut as sub-metering for each tenant in the building. Typically, eachmetering point will have a secondary node associated with it (thesenodes are not shown in FIG. 12, for simplicity), and from time to time,such a secondary node within a building will transmit data to thebuilding's main node (for instance, nodes 202 to 207). Other relativelysimple systems, associated with paucity of data transmissionrequirements may be associated with water level monitoring systems orfault annunciation (associated with various functions, such as watertowers, chillers and even central steam generators).

Such buildings may also have independent energy management and controlsystems with a plurality of monitored points, each such monitoring pointwill also have a secondary node associated with it, to transmit theinformation gathered. Obviously, data density associated with suchenergy management systems might be higher and have greater frequency oftransmission requirements than data associated with relatively simplemetering systems.

In yet some other buildings, there might be a “SCADA” (Supervisory,Control and Data Acquisition) system having associated with it its ownsecondary node or nodes, transmitting data to the building's main node,to be repeated by other main nodes until such data stream reaches itsdestination at the central node.

Other data that could be transmitted in the link layered network arerelated to electronic security and surveillance systems of variouskinds, from simple data stream associated with intrusion detection, tomore complex video images. Obviously, different type of systems areassociated with different data densities, but clearly, the data densitytransmission requirement would be much higher for SCADA and variousvideo security systems than for metering devices and simple intrusionalerts.

Typically, the only communication route to the network 200 fromsecondary nodes in a given building would be through the main nodeassociated with each building (for instance nodes 202 to 207).Communication from remote nodes (remote relative to the central node201) to the main nodes, will be, more often than not, through a seriesof other building nodes with the ultimate destination the central node.

A complex network as described in FIG. 12 is often the result of theconsolidation over many years of nodes having different technologies,packet capacities, broadcasting power etc. into a single network. Thenetwork of nodes also has to accommodate future nodes not yet availableor even conceived of yet. Thus if we look for instance at a main node202 in FIG. 12, it may have older technology, and is quite acceptablefor transmitting infrequent and short messages from a large number ofsecondary nodes (not shown) within the building, relating to waterlevels and even meters readings. However that node 202 cannot be used bythe main node 203, which is associated with more modern secondary nodesin the building transmitting higher capacity packets, for instance, froma SCADA system, or a video security surveillance systems. Thus, due toits higher packets capacity, the main node 203 messages reach thecentral node 201 through node 205. This is accomplished automatically inthe link layered network of the present invention as described above.Furthermore, if node 205 would become incapacitated either due to powerfailure, or even due to excess utilization, the system willautomatically, and without intervention from a human operator, adapt tothe new situation and, send the packets originating at 203 through analternative route, involving for instance, the main nodes 206, 207 and204 (assuming that all these nodes have packet capacities sufficient tohandle the capacity of the main node 203).

Having described in general the invention and some of its preferredembodiments in detail, it will now be obvious to those skilled in theart that numerous modifications can be made therein without departingfrom the scope of the invention as defined in the following claims.

What is claimed is:
 1. A method of preventing network congestion uponrestart of a wireless link layered network comprising a plurality oftransceivers at respective nodes which route communications from anynode to a then central node of the network and wherein saidcommunications are in a form of information packets transmitted from onenode to another, said method comprising stratifying reestablishment ofcommunication among said nodes whereby restart is effected layer bylayer, and within each link layer level, restart time is randomized. 2.A method of keeping operational a wireless link layered network withoutoperator intervention, comprising promulgating into the network, inresponse to changes at any node of the network, information as to suchchanges via message acknowledging system control and modifying message(SCMM), and assuring that only the node eliciting such an SCMM uniquelyacts upon said information, providing the SCMM originated from a nodehaving a link layer equal or lower than the eliciting node.
 3. A methodof keeping operational a wireless link layered network according toclaim 2, further comprising dynamically and without the intervention ofan operator rerouting messages to parts of the network that are lesscongested, said rerouting being effected by including in the SCMM ameasure of the utilization rate of the node originating the SCMM, and ifsaid utilization rate exceeds a preset level, rerouting messages aroundsaid SCMM originating node.
 4. A method of reducing congestion in awireless link layered network dynamically and without the interventionof an operator, wherein said wireless link layered network comprises aplurality of transceivers at respective nodes, each node successfullyreceiving an information packet eliciting as an acknowledgment a systemcontrol and modifying message (SCMM), said method comprising having allnodes that capture an SCMM from a node having a high utilization rateexceeding a preset level, remove said SCMM originating node from theirrespective routing lists, provided that the link layer level of the nodeoriginating the SCMM is equal or lower than each respective nodecapturing said SCMM.